Is there a danger that current welfare policies, unaided by eugenic foresight, could lead to the genetic enslavement of a substantial segment of our population? The possible consequences of our failure seriously to study these questions may well be viewed by future generations as our society's greatest injustice to Negro Americans" (Jensen, 1969, p. 95).
o said Arthur Jensen in 1969 in a Harvard Educational Review article on race and general intelligence. General intelligence is often called IQ for short. In the most controversial parts of The Bell Curve, a book written for the general reader, Richard J. Herrnstein and Charles Murray present much the same theories and general concerns as did Jensen with regard to Black cognitive intelligence, while extending the analysis to include Latinos. They greatly expand on the evidence, present possible causal links between IQ and socially undesirable behaviors, and at the end of the book suggest implications for public policy. They are especially worried about a supposed downward pressure on the distribution of IQ in the United States, which they call dysgenic pressure. Dysgenic is a term borrowed from population biology. As does Jensen, the authors believe that Blacks "are experiencing even more severe dysgenic pressures than Whites" (p. 341). Part of the problem may be differences in reproductive strategies among the races, according to J. Philippe Rushton's theory discussed in the book (pp. 642-643). Herrnstein and Murray mention Rushton's theory that Blacks have the largest genitals and the highest frequency of sexual intercourse among the three major races (p. 642). Consistent with customary academic standards of scholarly objectivity and neutrality, Herrnstein and Murray reserve judgment on whether Rushton is right or wrong: "We expect that time will tell whether it [Rushton's theory] is right or wrong in fact" (p. 643).
In addition to supposed downward pressures on the distribution of intelligence in this country produced by high fertility rates in Blacks, Herrnstein and Murray believe that Latinos are also experiencing more severe dysgenic pressures than Whites (p. 341) and that Latino immigration is putting downward pressure on the distribution of American national intelligence. So should we be worrying about dysgenic pressure on our national cognitive intelligence? They conclude, "Putting the pieces together--higher fertility and a faster generational cycle among the less intelligent and an immigrant population that is probably somewhat below the native-born average--the case is strong that something worth worrying about is happening to the cognitive capital of the country" (p. 364).
The authors present a large number of research analyses that they performed themselves, in which they pit parental socioeconomic status (SES) against IQ on a variety of economic and social behaviors. They conclude that the major cause of economic and social behaviors is IQ, not SES. The authors' research analyses are based on data collected in the National Longitudinal Survey of Youth (NLSY). None of their research analyses on the relation between IQ, SES, and social behaviors has ever been published in peer-reviewed scientific journals. The Bell Curve is written for the general reader and does not assume that the reader has had a course in statistics. The authors have even included an appendix for those readers who are sure they can not learn statistics, titled "Statistics for People Who Are Sure They Can't Learn Statistics" (Appendix 1, pp. 553-567). Scientists first publish their research in peer-reviewed scientific journals, not in books written for the general reader who may not have the technical background needed to detect flaws in data and misinterpretations of data analyses. It is inappropriate for a scientist to do otherwise.
Herrnstein and Murray's research analyses--never published in peer-reviewed scientific journals--investigate the relation of IQ and SES to marriage, to divorce, to illegitimacy, to welfare dependency, and to parenting. They conclude that IQ is the primary problem, not SES: "People with low cognitive ability tend to be worse parents" (p. 232). The authors believe that low birth weight and high infant mortality are indications of poor parenting and are probably caused by "prenatal negligence" (p. 233) on the part of mothers with low cognitive ability rather than inadequate prenatal medical care on the part of society. They also present unpublished research analyses on the relation between crime and low cognitive intelligence, and between civility and high cognitive intelligence. "A smarter population is more likely to be, and more capable of being made into, a civil citizenry" (p. 266), according to the authors.
In the final part of The Bell Curve, titled "Living Together," Herrnstein and Murray propose a solution to the supposed dysgenic downward pressures on our national intelligence caused by the large number of children born to "low-IQ women," and to the recent large-scale Latino immigrations to the United States. They argue that America's current fertility policy "subsidizes births among poor women, who are disproportionately at the low end of the intelligence distribution" (p. 548). They seem to urge eugenic foresight to counteract dysgenic pressure: "We urge generally that these policies, represented by the extensive network of cash and services for low-income women who have babies, be ended" (p. 548). With regard to the supposed dysgenic effects of Latino immigration on national intelligence, their central thought about immigration "is that present policy assumes an indifference to the individual characteristics of immigrants that no society can indefinitely maintain without danger" (p. 549). "But," they conclude, "we believe that the main purpose of immigration law should be to serve America's interests" (p. 549). For those members of groups who will not be excluded from the American dream by eugenic foresight or new immigration laws, Herrnstein and Murray propose "that group differences in cognitive ability, so desperately denied for so long, can best be handled--can only be handled--by a return to individualism" (p. 550).
Who are the authors of The Bell Curve? Are they right? The first author, Richard Herrnstein, was a professor of psychology at Harvard University for 36 years. He died a very short time ago. One would presume that The Bell Curve represents Herrnstein's final summing up of a lifetime of objective scholarly research published in peer-reviewed scientific journals on the genetic basis of IQ. Regrettably, the media seem to be totally unaware of the fact that the deceased Harvard professor never published any scientific research on the genetic basis of IQ and its relation to race, poverty, or social class in peer-reviewed scientific journals in his entire 36-year academic career. Richard Herrnstein's actual area of expertise is the experimental analysis of decision making in pigeons and rats, and he never studied the genetic basis of any behavior in those laboratory animals. The first presentation of his theory on the genetic basis of IQ, social class, and poverty appeared in a magazine article titled "I.Q." published in the September 1971 issue of the Atlantic Monthly magazine. As we all know, scientists publish their data and theories in peer-reviewed scientific journals or in peer-reviewed technical books, not in popular magazines or in nontechnical books written for the general reader.
In 1973, Herrnstein published a nontechnical Atlantic Monthly Press book titled I.Q. in the Meritocracy that expanded on his theory of the genetic basis of IQ and poverty. Herrnstein had never collected data on IQ, so the book drew on the work of others, especially the "data" of Sir Cyril Burt. According to Leslie Hearnshaw (1979), Burt's biographer and distinguished historian of British psychology, Burt had probably invented much of his highly cited data on the genetic basis of IQ. While doing research on Burt's data for an article that I later published in Science (1978), I discovered that Herrnstein had in fact laundered Burt's own descriptions of Burt's widely publicized and highly cited study "Intelligence and Social Mobility" (Burt, 1961). Burt had described his own study "merely as a pilot inquiry" (p. 9) and his data as "crude and limited" (p. 9). Burt had not even reported the number of subjects he had tested in his crude and limited study. In describing Burt's study, however, Herrnstein (1973) failed to tell the reader about the deficiencies that Burt, himself, had mentioned. In addition, Herrnstein (1973) said Burt's sample size was "1,000" (p. 203), later revising that figure to "40,000" in response to criticism. In reply to a critical letter by Jerry Hirsch (1975), Herrnstein (1975) revised his 1973 figure: "It is true that Burt's sample was 40,000, not 1,000 as I said" (p. 436), while failing to acknowledge that Burt had never reported the number of subjects he had tested. Leon Kamin (1974) appears to have been the only psychologist to notice and publicly report that Burt had failed to give the sample size of his celebrated 1961 study of IQ and social mobility. Presumably, Herrnstein and other psychologists who had publicized the results of that study had never noticed that Burt had not reported the sample size of his famous study.
The second author of The Bell Curve, Charles Murray, has a doctorate in political science from the Massachusetts Institute of Technology and is currently a Bradley Fellow with the American Enterprise Institute, a conservative research group in Washington, DC. Murray often publishes his research and theories in The Public Interest (e.g., Murray, 1994), a neoconservative magazine edited by Irving Kristol, also a fellow of the American Enterprise Institute and sometimes considered the founding father of neoconservatism (Atlas, 1995). In an article recently published in The Public Interest, Murray listed the first priority of his political agenda: "And so I want to end welfare" (1994, p. 18). Inasmuch as the media sometimes refer to The Bell Curve as Murray's book, perhaps the book represents Murray's summing up of a body of objective scholarly research that he had published in scientific journals on the genetic basis of IQ and poverty. But like his coauthor Richard Herrnstein, Murray has never conducted or published any research in scientific journals on the genetic basis of IQ and poverty in his entire career.
The Bell Curve is not a scientific work. It was not written by experts, and it has a specific political agenda. Still, it is possible that the major scientific premises of the book may be correct. If two monkeys were put before a typewriter, it is theoretically possible for those two monkeys to produce a Shakespearean sonnet. Perhaps Herrnstein and Murray produced a valid scientific work. I will now evaluate the major premises of The Bell Curve.
In 1972, Leon Kamin exposed the empirical unsoundness of the most important evidence in support of the IQ hereditarian position, Sir Cyril Burt's data (Hearnshaw, 1979). He later published his results in a book attacking Burt's data as well as the secondary sources who publicized those data (Kamin, 1974). In 1979, Leslie Hearnshaw (1979) published a biography of Burt in which he concluded on the basis of personal diaries and other material that it was highly likely that Burt had fabricated some of his most celebrated data. Hearnshaw, distinguished historian of British psychology, delivered the memorial address at Burt's Memorial Service and was later asked by Marion Burt, Burt's sister, to write a full-length biography of Burt. The result was the well-known Cyril Burt: Psychologist (1979). In their discussion of the Burt affair, Herrnstein and Murray suggest that some of Burt's "leading critics were aware that their accusations were inaccurate" (p. 12), suggesting a possible conspiracy against Burt. There is, however, no mention whatsoever of Hearnshaw's book in their half-page synopsis of the Burt affair, and Hearnshaw's book does not appear anywhere in their 57-page bibliography of references. This misrepresentation of the Burt affair by omission of important historical facts is not uniquely associated with The Bell Curve. In 1982, Richard Herrnstein published an article in The Atlantic Monthly in which he attacked the media for misrepresenting the evidence in the IQ controversy (Herrnstein, 1982). In that magazine article, the Harvard professor wrote "that most psychometricians had stopped trusting Burt's data years before, partly because of inconsistencies first noted in a 1974 article by Arthur Jensen" (p. 70), while omitting any mention of Leo Kamin, the psychologist who in reality first noted inconsistencies in Burt's data.
The distribution of IQ test scores cannot be expected to follow a bell curve unless it is constructed by the tester to do so (Dorfman, 1978). The shape of the distribution of IQ test scores will depend on the average difficulty of the test items as well as their intercorrelations. The high item intercorrelations in IQ tests imply that the IQ distribution can take a variety of shapes. The central limit theorem does not apply to random variables with positive intercorrelations (Lamperti, 1966). Frederic Lord (1952), one of the fathers of modern test theory and former president of the Psychometric Society, gave results on this question: "The results given are sufficient to show that the distribution of test scores cannot in general be expected to be normal, or even approximately normal. The question naturally arises as to what possible shapes the frequency distribution fs, as given in (76) [Lord's Equation (76)], may assume. The answer is that this function may assume any shape whatsoever, provided the item intercorrelations are sufficiently high" (Lord, 1952, pp. 32-33). The symbol fs refers to the distribution of test scores.
The book uses factor analysis to infer the existence of a single hypothetical general factor of cognitive intelligence that is presumed to account for most of cognitive performance. One of the problems with factor analysis as a tool for determining the underlying structure of a system is that neither the factors nor the loadings are uniquely defined if you have more than one factor (Lawley & Maxwell, 1963), and it is difficult to determine if you have only one factor. In experimental cognitive psychology, factor analysis is virtually never used as a tool to determine the underlying cognitive structure. It is a tool for correlational cognitive psychology, not experimental cognitive psychology. I inspected the subject index of some well-known texts in experimental cognitive psychology and found that the term factor analysis never appears in the subject index (e.g., see Anderson, 1985; Matlin, 1994; Reed, 1982). Why not? Kendall and Stuart (1966) may provide the answer: "Application of the same technique [factor analysis] to physical systems very often results in weighted sums of variables to which no clear interpretation can be given" (p. 310). In short, "The main difficulty, as a rule, is to know what the results mean" (p. 310), Kendall and Stuart point out.
The most direct way of estimating heritability is from data on monozygotic twins reared apart (MZA) and separated in early infancy (Bouchard, Lykken, McGue, Segal, & Tellegen, 1990). This MZA design allows for the estimation of heritability if the following major assumptions are met: (a) environments are a random sample from the population of environments, (b) genotypes are a random sample from the population of genotypes, (c) there is no genotype-environment correlation, and (d) there is no genotype-environment interaction. If the pairs of MZAs differ in age, then these assumptions will not be met. If these assumptions are met, then the intraclass correlation between IQ scores of MZA twin pairs directly measures heritability. Sir Cyril Burt's (1966) study of 53 MZAs appears to have met the first three assumptions. Unfortunately, Burt's data appear to have been invented (Hearnshaw, 1979). Bouchard et al.'s (Minnesota) survey of MZAs provides the next best data set. Unfortunately, to the best of my knowledge, the detailed case-study records of the Minnesota MZAs have never been released and have therefore not been subjected to public scrutiny to determine the degree to which assumptions have been met and the degree to which the MZAs told the truth to the Minnesota group. Finally, if there is genotype-environment interaction--then the fourth assumption is not met--and heritability is undefined. But this is the most controversial assumption underlying the MZA design. Herrnstein and Murray present no convincing evidence to justify the fourth assumption.
The authors have made a fundamental error well-known by professional geneticists. It is sometimes called "Jensen's error." Jensen made that error in his famous 1969 Harvard Educational Review article. The critical importance of that error was first clearly illuminated by Roger Milkman, a professor of biology at the University of Iowa and a world authority on population genetics and evolutionary biology. The article, "A Simple Exposition of Jensen's Error," was published in the Journal of Educational Statistics in 1978 (Milkman, 1978). Melvin Novick was editor of that journal when Milkman's article was published. Novick, professor of statistics and education at the University of Iowa at the time, later became president of the Psychometric Society. What is Jensen's error? It is that within-race heritability has no implications for between-race heritability. The Bell Curve is therefore flawed with regard to inferring between-race heritability in IQ from within-race heritability in IQ.
Herrnstein and Murray use logistic regression to determine which is more important--IQ or SES--in determining
socially undesirable behaviors. Logistic regression is a form of regression in which the dependent variable is binary.
In all of their analyses, they assume a simple additive model in which the logit (a transform of the sample proportion)
is assumed to equal B0 + B1IQ + B2SES + B3 age + random residual [numbers after Bs should read as subscripts]. They assume
no IQ-SES interaction. They use the standardized beta weights to determine the relative importance of IQ and SES in
determining the probability of various undesirable or desirable behaviors. Unfortunately, IQ and SES are highly intercorrelated
There are two major problems with Herrnstein and Murray's attempts to determine whether IQ or SES is more important. First, there is the collinearity problem. Weisberg (1985) describes the collinearity problem in linear regression: "When the predictors are related to each other, regression modeling can be very confusing. Estimated effects can change magnitude or even sign depending on the other predictors in the model" (p. 196). Next, there is the problem of deciding that the predictor with the largest standardized beta weight is the most important. Weisberg describes why this approach is faulty: "Unfortunately, this logic is faulty because the scaling depends on the range of values for the variables in the data" (p. 186). Perhaps these are the reasons why Herrnstein and Murray never published their logistic analyses in peer-reviewed journals.
Were Herrnstein and Murray as lucky as the proverbial monkeys at a typewriter? That depends on your point of view.
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Richard J. Herrnstein (deceased) was Edgar Pierce Professor of Psychology at Harvard University (Cambridge, Massachusetts) and is author of IQ in the Meritocracy and coauthor, with J. Q. Wilson, of Crime and Human Nature and, with E. G. Boring, of A Sourcebook in the History of Psychology. Herrnstein is coeditor, with R. C. Atkinson, G. Lindzey, and R. D. Luce, of Stevens' Handbook of Experimental Psychology, Vol. 1: Perception and Motivation, and Vol. 2: Learning and Cognition (2nd ed.); and, with M. L. Commons, S. M. Kosslyn, and D. B. Mumford, of Quantitative Analyses of Behavior, Vol. 8: Behavioral Approaches to Pattern Recognition and Concept Formation, and Vol. 9: Computational and Clinical Approaches to Pattern Recognition and Concept Formation.
Charles Murray, currently a Bradley Fellow at the American Enterprise Institute, is author of Losing Ground: American Social Policy 1950-1980.
Thomas J. Bouchard, Jr., professor of psychology at the University of Minnesota (Minneapolis) and director of the Minnesota Center for Twin and Adoption Research, is immediate past president of the Behavior Genetics Association and American Psychological Association Distinguished Scientist Lecturer for 1995. Bouchard is author of the chapter "The Genetic Architecture of Human Intelligence" in P. E. Vernon (Ed.) Biological Approaches in the Study of Human Intelligence and of the chapter "IQ Similarity in Twins Reared Apart: Findings and Responses to Critics" in the forthcoming R. J. Sternberg and E. L. Grigorenko (Eds.) Intelligence: Heredity and Environment. Bouchard is coeditor, with P. Propping, of Twins as a Tool of Behavior Genetics.
Donald D. Dorfman, professor of psychology and radiology and faculty member in the graduate program in applied mathematical and computational sciences at the University of Iowa (Iowa City), is author of the chapter "Group Testing" in S. Kotz and N. L. Johnson (Eds.) Encyclopedia of Statistical Sciences, Vol. 3 and coauthor, with J. T. Cacioppo, of the chapter "Waveform Moment Analysis: Topographical Analysis of Nonrhythmic Waveforms" in J. T. Cacioppo and L. G. Tassinary (Eds.) Principles of Psychophysiology: Physical, Social, and Inferential Elements.